1. Field of the Invention
The present invention relates to a semiconductor package with ultra-multipin structure produced by joining a semiconductor chip to a new leadframe and the manufacturing method.
2. Description of Related Art
FIG. 5 shows a semiconductor package which can be connected to a wiring board and others via an organic substrate provided with a protruded electrode such as a solder ball.
As shown in FIG. 5, a semiconductor chip 51 is mounted on the surface of a multilayer organic wiring substrate 50 consisting of two to six layers and formed by organic material. The electrode of this semiconductor chip 51 and a wiring film 52 formed on the surface of the multilayer organic wiring substrate 50 are connected by wire bonding using a gold wire 53 and others for example.
solder ball 55 which functions as a protruded electrode and is electrically connected to the wiring film 52 on the surface via a through hole 54 is provided on the rear of the multilayer organic wiring substrate 50 and this solder ball 55 is protruded from a solder resist film 56. The semiconductor chip 51 is sealed with sealing resin 57 together with the gold wire 53.
The solder ball 55 formed on the rear of a semiconductor package 58 constituted as described above is connected to a circuit wiring board 59. The multilayer organic wiring substrate 50 is often called a ball grid array (BGA) because multiple solder balls 55 are arranged in the shape of a grid and the semiconductor package 58 using this multilayer organic wiring substrate 50 is called BGA package.
There is a limit to reduce pitch between electrode pads on the side of the semiconductor chip 51 because the electrode of the semiconductor chip 51 and the wiring film 52 of the multilayer organic wiring substrate 50 are connected by wire bonding in this BGA package 58.
There are the following problems because a method of physically placing a so-called solder ball is adopted to form an electrode on the side of the multilayer organic wiring substrate 50:
(1) When the solder ball 55 is set in a predetermined position, misregistration often occurs.
(2) The size of the solder ball 55 is not fixed because the ball is selected using a sieve, a mesh and others.
(3) There is a limit in reducing the array pitch of the solder balls 55.
(4) The uniformity of the size of the solder ball 55 and formation by electroplating which enables the reduction of pitch are disabled because the base of the multilayer organic wiring substrate 50 is a base material.
(5) There is a limit to the composition of the solder ball 55.
Therefore, this applicant proposed a semiconductor package provided with ultra-multipin structure formed by joining a new leadframe and a semiconductor chip. FIG. 6 shows the structure of this semiconductor package and the semiconductor package is manufactured as follows:
First, to manufacture a semiconductor package 60 shown in FIG. 6, multiple leads 61 are formed on the surface of a metallic base not shown in FIG. 6 and prepared beforehand by copper electroplating, a polyimide film 62 for holding each lead 61 in a part except the inner lead section 61a is formed and further, a solder resist film 63 is formed.
Next, a protruded electrode 64 is formed in the outer lead section 61b of each lead 61 by electroplating, afterward the metallic base is selectively removed with the peripheral coupled portion left and hereby, a leadframe 65 in which each lead 61 is separated is obtained.
Next, a semiconductor chip 67 is joined to the inner lead section 61a of the lead 61 via a bump 66 and afterward, the body of a package 69 is stuck on the rear of the lead 61 except the inner lead section 61a via an adhesive layer 68. Finally, the semiconductor chip 67 housed in the body of the package 69 is sealed with resin 70 and further, an individual semiconductor package 60 is obtained by removing the coupled portion of the leadframe 65. In this case, multiple protruded electrodes 64 are formed and arranged in the shape of a grid around the semiconductor chip 67.
According to this semiconductor package 60, the lead 61 can be minutely patterned by forming the lead 61 and the protruded electrode 64 by electroplating using the metallic base. The protruded electrode 64 is formed in a right position, the size of each protruded electrode 64 is unified, pitch between protruded electrodes 64 can be reduced and the miniaturization of LSI and increasing the number of pins to ultra-multipin structure are enabled.
However, in the constitution of this semiconductor package 60, as the polyimide film 62 for reinforcing a lead and the solder resist film 63 for protecting a lead are overlapped on the lead 61 and difference in a level is made in the overlapped portion, there are the following problems:
That is, as a portion formed by the overlapped polyimide film 62 and solder resist film 63 is locally a cavity as shown in FIG. 7, the lead 61 is locally etched because of the existence of the hollow portion 71 and disconnection may be caused if the metallic base is selectively etched in the package manufacturing process.
When the solder plated ball is formed, a chemical such as a plating agent infiltrates from a location shown by a letter A in FIG. 7, is collected in the hollow portion 71, the failure of deposition occurs around it and an alloy layer may be formed. As this alloy layer produced due to the failure of deposition is formed between leads 61 and is left without being etched even when the metallic base is selectively etched, it causes a short circuit between the leads.
Further, in the final leadframe cleaning process, a chemical such as a plating agent is left and it causes stain and failure.